Rabbit erythrocytes release ATP and dilate skeletal muscle arterioles in the presence of reduced oxygen tension

In skeletal muscle, oxygen (O-2) delivery to appropriately meet metabolic need requires mechanisms for detection of the magnitude of O-2 demand and the regulation of O-2 delivery. Erythrocytes, when exposed to a decrease in O-2 tension, release both O-2 and the vasodilator adenosine triphosphate (ATP). The aims of this study were to establish that erythrocytes release ATP in response to reduced O-2 tension and determine if erythrocytes are necessary for the dilation of isolated skeletal muscle arterioles exposed to reduced extraluminal O-2 tension. Rabbit erythrocytes exposed to reduced O-2 tension in a tonometer (n = 5, pO(2) = 27 +/- 3, p < 0.01) released ATP in response to reduced O-2 tension. ATP release increased in proportion to the decrease in O-2 tension. The contribution of erythrocytes to the response of skeletal muscle arterioles to reduced extraluminal O-2 tension was determined using isolated hamster cheek pouch retractor muscle arterioles perfused with buffer (n = 11, mean diameter 52 +/- 3 mu m) in the absence and presence of rabbit erythrocytes. Without erythrocytes, arterioles did not dilate when exposed to reduced extraluminal O-2 tension (pO(2) = 32 +/- 4 mmHg). In contrast, when rabbit erythrocytes were present in the perfusate (hematocrit 15%), the same decrease in O-2 tension resulted in a 20 +/- 4% dilation (p < 0.01). These results provide support for the hypothesis that erythrocytes, via their ability to release O-2 along with ATP in response to exposure to reduced O-2 tension, can participate in the matching of O-2 delivery with metabolic need in skeletal muscle.